30 Jun, 2013
Fuse in action
PRESENTATION: When charge carriers pass from a high potential zone to a low potential zone energy is liberated, producing the heating of the elements of a circuit. This effect can become dangerous.
- The Fuse-Wires-in-Parallel Problem, William Layton, Phys. Teach. 51, 38 (2013)
- Cascading failure in holiday lights, Aaron Schuetz, Phys. Teach. 51, 186 (2013)
INTRODUCTION: A fuse is considered one of the best protection for circuits because of its operational velocity, high interruptive capacity, and limiting behavior towards current passing. In the past, it was very common that when there was a short circuit, this would provoke fires and damages in installations or in electrical equipment. To solve the lack of an installation protective device, Thomas Alva Edison invented the first electrical fuse in 1880.
OBJECTIVE: To show the behaviour of a fuse with a charge that is higher than acceptable.
MATERIALS: fuse of 0.5 A 125 V, flexible cable (phase and neuter), socket, 60 W light bulbs, plug, connecting switches.
SETUP: We connect the 4 sockets in parallel to the fuse by means of the flexible cables and the 4 sockets and then we connect it to the electric power supply. Then we will put the light bulbs in the sockets until the intensity is big enough for the fuse to go.
EXPLANATION: A fuse is a device formed in this case, by a lead wire (a low melting point and resistivity material). When a short circuit takes place (there is a potential or tension difference in the terminals and no electrical impedance) the intensity tends to the infinite and the connected devices are at risk due to the heat that is generated by such intensity due to the Joule effect.
I = V / Z ( si Z=0, I = ∞)
To avoid it, a fuse is placed at the beginning of the installation (resisting a I≤0,92 A). When we place the electric bulbs in parallel we increase the intensity of the current until there is an intensity that is higher than the tolerated by the fuse. At this moment, due to the Joule effect, the fuse melts/breaks interrupting the electricity flow to protect the rest of the circuit from suffering any harm.
CONCEPTS: charge, current intensity, melting (rupture) point, resistivity, Joule effect, Ohm’s law.
- WAKE FOREST UNIVERSITY
- BERKELEY UNIVERSITY
- WASHINGTON STATE UNIVERSITY
- UNIVERSIDAD POLITECNICA DE VALENCIA
- Fowler R.J., Electricidad: principios y aplicaciones, Reverté, 1992.
- Onsalo F., Electrotecnia: ciclos formativos, Donostiarra, 1999.
- Fink D.G., Wayne Beaty H., Carroll J.M., Manual práctico de electricidad para ingenieros, Reverté, 1984.
STUDENTS 2012 2013: Iván Díaz, Alejandro Espiño, Víctor Lago, Alba Souto.
LINK pdf STUDENTS (In Spanish):